The United States National Holocaust Museum in Washington made the photos public after obtaining them from a US officer who found them in an apartment in Frankfurt. In a statement, the museum's director, Sara Bloomfield powerfully articulated what makes these images so chilling.

"These unique photographs vividly illustrate the contented world they enjoyed while overseeing a world of unimaginable suffering," she said. "They offer an important perspective on the psychology of those perpetrating genocide."

Judith Cohen, the director of the museum’s photographic reference collection, said "precisely what makes [the photos] so horrible" is the fact that they don't show anything confronting or heinous. These people appear "normal" - their faces aren't the faces of killers.

The album was found to belong to Karl Höcker, the man pictured playing with his dog. He was an SS commander and adjutant to the commander of Auschwitz concentration camp. In 1963, Höcker stood trial for his crimes at Auschwitz, and said, "I had no possibility in any way to influence the events and I neither wanted them to happen nor took part in them."

Ultimately, he spent seven years in prison for aiding the murders of 1,000 Jews.

The most well-known individual photographed is Dr. Josef Mengele, who became known as the 'Angel of Death' for the he tortured those at the death camp, conducting horrific medical experiments. He exposed children to surgeries with no anesthesia, injected chemicals into their eyes in an attempt to change their eye colour, and removed the limbs and organs of twins in archaic surgical procedures.

Here, he takes a break with fellow officers:

Officers take a break. The man second from the left is Josef Mengele - the Nazi doctor of Auschwitz.

The images convey the chilling apathy of those carrying out unimaginable horrors - and remind us of the potential for terrifying outcomes when prejudice and racism prevail in any society.